The present invention relates generally to systems for controlling engine and/or vehicle operation, and more specifically to such systems operable to control engine and/or vehicle operation during vehicle braking conditions.
Many modern heavy duty tractor trucks include engine compression brakes operable to apply retarding torque to internal combustion engines carried by the trucks during prescribed operating conditions. Such engine compression brakes are typically used to assist in decreasing engine and/or vehicle speed in addition, or alternatively, to the vehicle service brakes. Engine compression brake technology has been well received and is widely used, particularly in the heavy duty diesel engine industry, and operational details thereof are well known.
When a tractor truck operator encounters a steep downhill or negative grade, known technology typically requires the operator to carefully exercise control over the engine compression brakes, service brakes and downshifting of the vehicle transmission to thereby maintain a controlled descent down the hill. As this term is used herein, xe2x80x9ccontrolled descentxe2x80x9d is understood to define a downhill vehicle operating condition wherein engine or vehicle speed is maintained substantially at a target engine or vehicle speed. Such descents, however, are largely a function of the vehicle operator""s experience, and a runaway vehicle condition may result when an operator loses control over engine/vehicle speed while descending the grade. Most steep negative grades accordingly include run-off areas that provide a steep uphill vehicle path or other means for maneuvering the vehicle out of harm""s way while also providing for increasing engine/vehicle retarding force due to the steep positive incline or other vehicle slowing/stopping means. Concern over runaway vehicle conditions may be heightened as transmissions in heavy duty tractor trucks become more automated since vehicle operators may become increasingly reliant on automated shifts, and hence the capability of manually downshifting to a numerically lower gear may become increasingly overlooked. Currently, no systems are known for automatically controlling engine/vehicle speed to thereby provide for a controlled descent under potential runaway vehicle conditions.
There also exist other conditions where it would be desirable to provide for a controlled descent down a negative grade at an engine/vehicle speed that is different from current engine/vehicle speed conditions. As a specific example, a vehicle operator may crest a steep downhill grade at a first vehicle speed (e.g. 55 mph), and desire to descend the grade at a lesser second vehicle speed (e.g. 40 mph) due to current weather conditions, changing speed limit restrictions or the like. While the vehicle operator may have no trouble in achieving the lesser second vehicle speed via proper control over engine compression brakes, service brakes and/or transmission gear shifting, no systems are currently known for automatically providing for a controlled descent down a negative grade at a selected engine/vehicle speed.
What is therefore needed is a system for automatically controlling engine/vehicle speed to thereby provide for a controlled descent down a negative grade. Such a system should ideally provide for a controlled descent under potential runaway vehicle conditions and further under conditions specified by the vehicle operator to thereby provide for a controlled descent at a desired engine/vehicle speed.
It would further be desirable to provide for controlled vehicle deceleration during ordinary braking conditions. By controlling the retarding torque of the vehicle driveline under such conditions, less reliance is placed on the service brakes, thereby providing for safer and more controlled vehicle stopping events while also extending service brake life. As used herein, the term xe2x80x9cvehicle drivelinexe2x80x9d is to be understood to include any component coupled to, and including, the engine carried by the vehicle that contributes to and/or transfers driving force to the vehicle wheels.
What is therefore additionally needed is a system for automatically controlling vehicle driveline retarding torque to thereby provide for controlled deceleration during vehicle braking events. Such a system should ideally be operable to selectively modulate vehicle driveline retarding torque as a function of desired braking force to controllably decelerate the vehicle while also minimizing service brake wear.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention.
One object of the present invention is to provide a system and method for controlling vehicle braking operation.
Another object of the present invention is to provide such a system operable to modulate the retarding torque of the vehicle driveline as a function of desired braking force such that the vehicle braking event is borne primarily by the vehicle driveline.
Yet another object of the present invention is to provide such a system that minimizes service brake wear by controlling vehicle braking events primarily through selective control of one or more of an engine compression brake, transmission downshift points and turbocharger wastegate.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.